ananyo writes: "The question of methane on Mars isn’t dead yet, but NASA’s Curiosity rover has at least put a first nail in the coffin.At a briefing on Friday, scientists on Curiosity announced that they had not detected methane with any confidence — though they left themselves some wiggle room for revision, saying that methane could be present at levels of less than 5 parts per billion.On Earth, life is responsible for the vast majority of the planet’s atmospheric methane, which exists at levels of about 1,700 parts per billion. If methane were detected on Mars, microbes could thus be invoked as its source, though trace amounts could also be produced via comet impacts or chemical reactions underground involving rocks and hot water."